A health worker who was the first person diagnosed in Britain with Ebola arrived at a London hospital from Scotland early on Tuesday for treatment after contracting the disease in West Africa.

The woman arrived at the Royal Free hospital, Britain's designated Ebola treatment center, in an ambulance accompanied by several police vehicles, a Reuters witness said.

“The latest update we have on the condition of the patient is that she is doing as well as can be expected in the circumstances,” Scottish First Minister Nicola Sturgeon said.

The BBC named the patient as Pauline Cafferkey, a nurse with 16 years' experience who normally worked at a Scottish health center. Sturgeon said she could not confirm the patient's identity for confidentiality reasons.

The hospital's 'High-level isolation unit' will allow doctors to treat the patient while she lies inside a plastic tent, limiting the scope for the disease, which is transmitted by contact with bodily fluids, to be passed to medical staff.

Prime Minister David Cameron was chairing a meeting of the government's emergency response committee to discuss the case, his office said.

The World Health Organization said on Monday that the number of people infected by Ebola in the three West African countries worst affected by the outbreak - Sierra Leone, Liberia and Guinea - had passed 20,000, with more than 7,842 deaths so far.

The British woman, a National Health Service worker who had been working in West Africa with the charity Save the Children, flew from Sierra Leone to Glasgow late on Sunday on a British Airways flight via Casablanca in Morocco and London's Heathrow.

She was diagnosed with the deadly virus on Monday after developing symptoms overnight and was initially treated at Scotland's Gartnavel Hospital. Local media said she is in her late 30s.

Low contagion risk

Scottish authorities have said the illness was diagnosed at an early stage, meaning the risk to others was considered extremely low, but they were investigating all possible contacts with the patient.

“I'm satisfied... that the procedures, the protocols, the things that we've been practicing now for months and months have now kicked in,” health minister Jeremy Hunt said.

Britain began screening passengers arriving from West Africa for symptoms of Ebola in October as part of its preparations for a case of the disease on British soil. Hunt said at the time that he expected to see “a handful” of cases arriving in Britain.

Earlier this year the Royal Free hospital successfully treated another British aid worker, William Pooley, who was flown home for treatment after being diagnosed with the virus in Sierra Leone.

Sturgeon said a second patient in Scotland was being tested for the virus after returning from West Africa, but had a low probability of having the virus, having had no known contact with infected people.

A third person was undergoing tests for the Ebola in Cornwall, England, and was being treated in an isolation unit, a statement from Public Health England said. The results of that test would take at least 24 hours, the statement said.

Around 200 people have been assessed or tested for the virus in recent months, Paul Cosford, Director for Health Protection at Public Health England, the government body handling Britain's response to Ebola, told the BBC.